1. Field of the Invention
The present invention relates to a surface mount type electronic component. More particularly, the present invention relates to a surface mount type electronic component in which electronic elements are mounted on a case substrate and a cap is fixed onto the case substrate so as to cover the electronic component.
2. Description of the Related Art
Recently, as the size of circuits continues to decrease, surface mount type (chip-type) electronic components have been widely used in place of components including leads. In conventional surface mount type electronic components as described in, for example, Japanese Unexamined Patent Application Publication No. 2000-286665, a piezoelectric resonance component includes a piezoelectric resonator that is mounted on a capacitor substrate and a cap that is mounted on the capacitor substrate. The capacitor substrate includes a plurality of stacked dielectric layers and first to third internal electrodes that are provided therein. The first internal electrode is provided in a different layer from those of the second and third internal electrodes, and the second and third internal electrodes are provided so as to be separated but disposed on the same layer. The first internal electrode opposes the second and third internal electrodes with a dielectric layer disposed between. First to third external electrodes are provided on the outer surface of both end portions and of the central portion of the capacitor substrate. Regarding the third external electrode provided on the outer surface of the central portion, the top surface portion thereof is omitted. The first to third external electrodes are electrically connected to the first to third internal electrodes, respectively.
In the surface mount type electronic component having the above-described structure, the first and second external electrodes provided on the top surface, the bottom surface, and the side surface of the capacitor substrate are continuous bands having the same width. That is, the spacing between the external electrodes on the top surface to which the piezoelectric element is connected and the spacing between the external electrodes on the bottom surface of a circuit substrate for mounting electronic components are the same.
However, the spacing between the external electrodes on the top surface of the capacitor substrate must be determined according to the length of the piezoelectric element mounted on the capacitor substrate, and the spacing between the external electrodes on the bottom surface of the capacitor substrate must be determined according to the land dimensions of the circuit substrate for mounting electronic components.
Recently, the length of piezoelectric elements has decreased. If, correspondingly, the spacing between external electrodes decreases, when these are mounted on a circuit substrate, problems, such as short-circuiting, occur.
If the spacing between external electrodes on the top and bottom surfaces are the same, the element length, the outside shape dimensions of the capacitor substrate and the land dimensions are limited, and a problem arises in that the degree of design freedom is greatly reduced. Additionally, the amount by which the size of electronic components can be reduced is severely limited.
In order to overcome the above-described problems, preferred embodiments of the present invention provide a surface mount type electronic component having outstanding freedom of design and a greatly reduced size.
According to a preferred embodiment of the present invention, a surface mount type electronic component includes a substantially rectangular case substrate, an electronic element mounted on the case substrate along the longitudinal direction, and a cap which is fixed to the case substrate so as to cover the electronic element, wherein first and second top-surface electrodes and first and second bottom-surface electrodes, which extend along the width direction of the case substrate, are provided and spaced apart on the top surface and the bottom surface of the case substrate, respectively, the first top-surface electrode and the first bottom-surface electrode are connected to each other via a first side electrode provided on a side surface of the case substrate, and the second top-surface electrode and the second bottom-surface electrode are connected to each other via a second side electrode provided on a side surface of the case substrate, the electronic element is electrically connected to the first and second top-surface electrodes, and the spacing d1 between the first and second top-surface electrodes differs from the spacing d2 between the first and second bottom-surface electrodes.
An electronic component is electrically connected between the first and second top-surface electrodes provided on the top surface of the case substrate. The first and second bottom-surface electrodes provided on the bottom surface of the case substrate are mounted on an electrode pad of the circuit substrate. In particular, since the spacing d1 between the top-surface electrodes of the case substrate differs from the spacing d2 between the bottom-surface electrodes, the spacing d1 of the top-surface electrodes is set to the most appropriate dimensions in accordance with the length of the electronic component, and the spacing d2 of the bottom-surface electrodes is set to the most appropriate dimensions in accordance with the spacing of the electrode pads. Therefore, the freedom of design is greatly improved, and the size is further reduced.
The spacing d1 between the first and second top-surface electrodes may be less than the spacing d2 between the first and second bottom-surface electrodes.
In preferred embodiments of the present invention, the spacings d1 and d2 are set as desired. However, the length of a piezoelectric element is often very short. If it is set that d1 greater than d2, the spacing d2 of the bottom-surface electrodes is too small, and when piezoelectric element is mounted on a circuit substrate, short-circuiting may occur. Therefore, by setting d1 less than d2, short-circuiting during mounting is prevented when mounting a short, small piezoelectric element.
The side electrode preferably includes a portion which continuously extends in the thickness direction of the case substrate from the top-surface electrode at the same width as that of the top-surface electrode and a portion which continuously extends in the thickness direction of the case substrate from the bottom-surface electrode at the same width as that of the bottom-surface electrode, and both portions are preferably joined in an intermediate portion of the case substrate in the thickness direction. That is, the first and second side electrodes provided on the side surface of the case substrate are preferably step-shaped.
More specifically, since the spacing d1 between the top-surface electrodes differs from the spacing d2 between the bottom-surface electrodes, if the side electrode provided on the side surface of the case substrate is aligned with the top-surface electrode, a deviation from the bottom-surface electrode occurs at the edge of the case substrate. Similarly, if the side electrode is aligned with the bottom-surface electrode, a deviation from the top-surface electrode occurs at the edge of the case substrate. The deviation of the electrode at the edge of the case substrate decreases conduction reliability. For this reason, it is preferable that the electrodes provided on adjacent surfaces with an edge in between have substantially the same width.
Accordingly, by joining, in an intermediate portion of the case substrate in the thickness direction, a portion of the side electrode, which continuously extends along the thickness direction of the case substrate from the top-surface electrode at the same width as that of the top-surface electrode, and a portion of the side electrode, which continuously extends along the thickness direction of the case substrate from the bottom-surface electrode at the same width as that of the bottom-surface electrode, the electrode deviation at the edge is eliminated, and thus the conduction reliability of the electrodes on the top and upper surfaces is greatly improved.
The electronic element may be a piezoelectric element. The case substrate preferably includes two capacitors incorporated therein. A third electrode is preferably provided between the first and second bottom-surface electrodes. One of the capacitors is connected between one of the first top-surface electrode and the first bottom-surface electrode, and the third electrode, and the other capacitor is connected between one of the second top-surface electrode and the second bottom-surface electrode, and the third electrode.
More specifically, in a Colpitts oscillation circuit, a phase compensating capacitor is connected between one of the electrodes of the piezoelectric element and the ground and between the other electrode and the ground. In the present preferred embodiment of the present invention, by incorporating these capacitors in the case substrate, a compact piezoelectric resonator for an oscillation circuit is obtained.
The case substrate preferably includes a plurality of stacked dielectric layers having internal electrodes provided thereon, or a chip-type capacitor may be provided separately.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.